you will have to create a scheduled task in your hosting control panel if you want to automatically regenerate sitemap from time to time (otherwise sitemap should be created manually).
The time depends on the page generation time mainly, since it crawls the site similar to search engine bots.
For instance, if it it takes 1 second to retrieve every page, then 1000 pages will be crawled in about 16 minutes.
Some of the real-world examples of big db-driven websites:
about 35,000 URLs indexed - 1h 40min total generation time
about 200,000 URLs indexed - 38hours total generation time